These studies were performed to help define the effects of carbon dioxide lasers on human coronary arteries in air. Specifically, changes in lasing parameters have important influences on the efficiency and thermal tissue effects using carbon dioxide lasers. Fresh human coronary arteries were studied employing a uniform methodology and we have concluded that short plus (less than 10-20 msec) C02 lasing generally results in better tissue ablation with symmetric craters associated with minimal circumferential charring and a small zone of thermal injury. Thus, short pulse C02 may be an appropriate laser source for in vivo angioplasty investigations.